Exploration of Cervical Problems Arising from Inappropriate Posture and. Improvement. By Li Nianlin. Director: Luo Leisheng

Transcription

1 Exploration of Cervical Problems Arising from Inappropriate Posture and Improvement By Li Nianlin Director: Luo Leisheng The High School Attached to Tsinghua University Abstract Many people have problems with their neck. One reason is the influence of inappropriate posture in our life and work that has received little attention, especially for high school students. Cervical problems usually do not have good outcomes in the short term, because most are caused by accumulated processes. Cervical problems are mainly related to the neck muscles. A habit of staying in an inappropriate posture for a long time, which is very common, can lead to neck pain and sometimes serious cervical injuries. This study analyzes how inappropriate posture, head-forward positioning, could cause cervical problems. A force analysis of the head forward position clearly shows that this posture generates greater stresses on both the neck and the muscles. The problem is addressed by a cervical care special pillow, which can be used for short periods or while sleep and is easy to carry. This pillow stops the problem from getting worse and so should be helpful to high school students. 1

2 Table of contents 1. Introduction Exploration natural cervical Samples of inappropriate posture Force analysis Rehabilitation Rehabilitation pillow Rehabilitating mechanism The inflatable pillow Rehabilitation process Additional advice Concluding remarks Reference 2

3 1. Introduction Cervical problems are commonly seen in daily life and this study topic was inspired by noticing my classmates studying in some strange positions quite different from our natural posture. Cervical problems are becoming more common in the younger generation [1, 2]. A senior once shared her experience and lessons on the first day of our high school life. She talked about the importance of appropriate posture and told us never to stay up late or study for a long time without moving, because she had developed cervical problems when she failed to care for herself. She also told us that cervical problems can cause many symptoms like headaches. So, I have been concerned about how studying in inappropriate position scan cause neck problems. One study [2] of cervical problems shocked me, particularly after I counted how many my classmates were in inappropriate positions while writing in class. I then realized that cervical problems are ubiquitous in today s world. Cervical problems can result in serious cervical diseases and even affect thoracic and lumbar spines. The problems are the result of a cumulative process that changes the cervical spine day by day. Therefore, we can easily relate a daily inappropriate posture and a bad cervical spine. For students, long periods doing homework and improper table heights can lead to bad study habits with inappropriate posture. This paper focuses on one common inappropriate position high school students often use the head-forward posture is one of the most common positions students choose while studying. This changes the cervical spinal curvature only in the vertical direction but causes neck pain. This study shows how the straightened cervical curvature can cause cervical problems using a structure based force analysis. Another purpose of this paper is to show how incorrect posture can damage the cervical spine curvature and how these changes in the cervical spinal curvature can cause neck pain by affecting the neck muscles and ligaments and changing the forces exerted by the neck muscles on the cervical spine. Since high school students can be very busy in school and most of their problems are not serious, a special pillow was developed to mold the cervical spine. The pillow can be used for short time or while sleeping. This solution stops the problem from getting worse and is easy and convenient to carry. Many papers [1, 2] have shown that cervical problems are very serious and focused on cervical paralysis and its treatments. However, in later on study I find out that cervical problems caused by inappropriate posture (such as head forward) can be easily solved in the beginning by using simple recovery training. This is perhaps not cervical disease but more like discomfort in the cervical region. Such discomfort is 3

4 common in high school students so this is a valuable study topic. 2. Exploration The head-forward position will certainly damage the cervical vertebra. The consequences of the inappropriate position can be seen in a force analysis. Evolution has given the body the best cervical curvature [4]. This paper compares force analyses of natural cervical vertebra and an inappropriately positioned vertebra. Generally, if someone knows his actions will hurt him, he will pay attention to this issue. Regarding the head-forward position, most high school students like my classmates do not know this will damage their spines. Actually, I myself always sit cross-legged and lean over my table during writing. People will try to adjust to avoid pain but most people including me do not know how bad posture can cause injury. Then, students get used to inappropriate positions and habits are difficult to change. This paper will show the superiority of the natural cervical curvature and the disadvantages of unsuitable posture to help students like me realize the importance of these problems. This study focuses on the anatomy of the human spine, particularly the cervical spine. The curvature of cervical spine is designed to hold the head and absorb shock. 2.1 Natural cervical spine In a natural cervical spine, the geometric centers of C1 and C7 are nearly in line with gravity. Thus, the weight of the head will not generate a torque. Since all the pressure can be held by the cervical vertebra, the neck muscles will relax. (A natural cervical spine is shown in Figs. 1 and 2). The cervical curvature then helps with shock absorption. The natural cervical shape is the best design to protect the muscles and bones, particularly the nerves inside of spine. Since the cervical curvature forms a shock-absorbing system, changes in the curvature can harm the bones and muscles, then nerves. 4

5 C1 C7 Fig. 1 Lateral view of the spine [4] Fig. 2 X-ray image showing a normal cervical spine [4] D1 Fig. 3 Diagram of the force analysis for a normal cervical spine, cervical spine picture from ref.5 ] As shown in Fig. 3, in a regular cervical spine the force supported by C7 in the vertical direction is simply the weight of the head and neck. The muscles are relaxed and the forces provided by the muscles can be ignored. Both the bones and the muscles are bearing least forces in this situation. D1 is the horizontal distance between a vertical line of head-neck gravity through C7 and the C7 center in a natural cervical spine. The ideal situation is that D1 is very small when the cervical position is normal with only small forces provided by the neck and cervical vertebra. Students often put their head forward when studying which straighten the cervical vertebra. Straightening of the cervical curvature causes the head to move forward and generates a torque. Since the bones provide the only supporting force, the pulling force provided by the neck muscles is needed to balance the torque generated 5

6 by head weight. As the head moves further forward, the moment arm increases which increases the forces and lengthens the muscles. As the muscles continue to be pulled, they eventually can t return and the neck ends up with muscular rigidity. 2.2 Samples of head-forward posture I discussed with my classmates about the head-forward posture. Several confirmed that their cervical spines were uncomfortable sometimes. The most common condition was a rigid neck. Figure 4-6 show some photographs of students as they were working then normal position. Many put their head forward without realizing it, because of the unsuitable heights of the tables or chairs. (a) side view (b) back view Fig. 4 Head-forward posture while working, subject 1. (a)side view (b)back view Fig. 5 Head-forward posture while working, subject 2. 6

7 (a) side view Fig. 6 Head-forward posture while standing subject 3. (b) back view (a) No cervical curve Fig. 7 X ray images of the head-forward posture (b) force and torque analysis The force diagram in Fig. 7(a) shows how the change in the cervical curvature generates an included angle between the cervical axis and the vertical. The problem in Fig.7 was a simplified cervical model as an angled line, running from the center of C1 to the center of C7. The neck muscles have rather complex shapes, but they are all next to the cervical vertebra and provide a pulling force F1. The bones provide a supporting force F2 which is parallel to F1. There the two forces create a couple which provides a torque to balance the torque due to the weight of the head and neck Force analysis of the head-forward posture The force analysis of the head-forward posture is divided into two cases. Cast1: forces on a straighten cervical spine 7

8 The head-forward posture can eliminate the natural curvature of the cervical spine. (a) force locations (b) Diagram Fig. 8 Force analysis of the straightened cervical spine: (mg is the weight of the head and neck, d1 is the distance between the center of C7 and the vertical line through the center of mass of the head and neck, d2 is the width of the cervical spine, F1 is the force provided by the neck muscles. (The widths of the muscles have been neglected.) The center of C7 is used to calculate the torques, so the supporting force acting on C7 (shown as N) does not generate a torque. The angle between the neck and the horizontal plane is a. The distance between C7 and H(the normal center of the head and neck)is L.) The main focus is the influences causing by head-forward. Since the shoulder inclination angle can affect the results, it should not be changed in the experiments. The line from C7 to H is shown in Fig. 8(b). The shoulders supply the force, N, to support the weight of the head and neck, so N is equal but opposite in direction to the weight. Since the directions of N and mg are not on the same line, the two forces will generate a torque. To balance the system, F1 and F2 should be equal and in the opposite directions. Both of these forces create a couple that makes the sums of the moments and the forces both zero. The generated torque can be expressed as: F1 d2 or F2 d2. Thus, these three forces are a simplified model of all the complex forces from the shoulder to the head and neck. The torque generated by F1 and F2 is related to the distance between the two forces and their magnitudes, but their directions can only be inferred. The model assumes that the cervical vertebra can only bear a supporting force and the muscles can only be in tension, so the directions of the two forces should be parallel to the cervical spine. The distance between them should then be width of the cervical spine. Force F1 is given by: mg D2=F1 d2 (1) D2=L cos a (2) F1=mg L cos a/d2 (3) 8

9 For a normal cervical spine, a is almost 90 degrees. Aa the cervical problem worsening, a will decrease and from Eq. (3), F1 will increase. This simple model shows how inappropriate posture will generate more force on both the cervical vertebra and the muscles. I found that most students have their head pushed forward degrees while writing, so a is degree. Generally, L=150 mm and d2=50 mm. Assumed an average student weight of 65 Kg, and that the weight of the head and neck is about 8% of the total mass then for a=80, F1=27.1 N, while for a=75, F1=40.4 N. Although the force is not very large, it will damage the muscles if you keep that posture for a long time. Case 2: Force analysis in reversed cervical flexure: As the cervical problems become worse, the cervical spine can flex in the wrong direction. To simplify the problem, the cervical spine is model by a section of a circle. The force analysis for the reversed cervical flexure does not differ much from the model for straightened cervical spine. The directions of F1and F2 do not change and the lengths of the cervical spine and the shoulder inclination angle are same. Thereby, I assumed that the line of the straightened cervical spine should be tangent to the circle. A picture for the reversed cervical flexure is shown in Fig. 9 (a). (a) reversed cervical flexure [2] (b) Diagram Fig. 9 Force analysis for case 2 In the reversed cervical flexure, H moves to H and I connects H and C7. The length between H and C7 is defined as L. In this case, θ is defined as the angle between H C7 and the horizontal plane. The vertical distance between the vertical through H and the C7 is D3. The other physical quantities were mentioned in case 1. Then: mg D3=F1 d2 (4) L is only slightly shorter than L, 9

10 D3=L cos θ L cos θ (5) However, θ is much smaller than α in case 1. Therefore: F1 mg L cos θ/d2 (6) Since θ is smaller than α, cos θ is bigger than cosa and D3 is also bigger than D2. F1 is larger in case 2 than in case 1. Thus, as F1 and F2 both become larger, the cervical vertebra and muscles will bear larger loads. As shown by the force analysis, not only will the muscles bear greater loads, but the pressure supported to C7 will also increase. These will more easily tire the spine. Furthermore, when the neck muscles do not have enough strength to balance the system, the shoulder and back muscles will have to help. Then the fulcrum will move from C7 to the thoracic spine or even to the lumbar spine. This will create a vicious cycle and the cervical problems can end up creating a hunchback. The taut muscles can cause compression on the nerves, so cervical problems can also cause nerve problems. Fig. 10 Muscles controlled by the cervical nerves [4] The diagram in Fig. 10 shows that cervical problems can influence the head, hands, neck and shoulder. Thus many health problems in daily life are rooted in the cervical spine. This analysis has shown how the neck muscles and the cervical vertebra will bear larger loads due to inappropriate posture. The disk between the cervical bones can then be compressed by the pressure. The neck muscles will then be stretched and 10

11 the cervical problems will worsen. Also many parts of the body are controlled by the nerves in the cervical spine, the neck problems can lead to many other problems such as headaches. 3. Rehabilitations Since high school students are very busy, they don t have time for special training to care for their cervical spine. However many students have cervical pain, so I have been thinking about a simple way to stop it from getting worse. 3.1 Rehabilitation pillow Cervical problems are very common in today s world, but the cervical curvature and muscle flexibility can improve by using a special pillow while sleeping or just resting. When I saw my father using a blood pressure monitor to measure his blood pressure, I had an idea s to put an inflatable bag into a pillow case to make a flexible pillow. Fig. 11 Blood pressure monitor with an inflatable bag 3.2 Rehabilitation Mechanism Figure 12 shows a pillow under the neck can be used to modify a straightened cervical spine. Neck Head Body Pillow Fig. 12 Rehabilitation mechanism with an inflatable pillow 11

12 Since the cervical spine can easily change shape, we need to provide a support to keep or improve the curvature. The inflatable pillow can be put under the neck. With the weight of the head used to generate a force to enlarge the cervical curvature. The head will be lifted off the bed for short period with the weight of the head is supported by the cervical spine and the pillow. The pillow should not be put under the head but under the cervical spine or the cervical spine will still be straightened while we sleep. If the pillow is too high, the excessive force may damage the vertebra or the disks, so the pillow should initially only be inflated a small amount while sleeping. Neck Head Body Pillow Fig. 13 Cervical curvature rebuilding mechanism The cervical curvature can be gradually rebuilt as shown in Fig. 13 with the pressure in the pillow slowly increased. The progress should be gentle to properly care for our cervical vertebra. If someone is doing cervical training which wake, his head should be lifted off the bed so as to provide greater pressure, but this can be uncomfortable. Therefore, the training time should not be too long and the pillow height should be carefully adjusted a little when the person has used that position for some time. While sleeping, the head should be on the bed to be more comfortable for sleeping. The pillow could then help the muscles relax and return to go their natural length. The pillow can also help maintain the natural cervical curvature and stop changes in the cervical shape. 3.3 The inflatable pillow In the beginning, I planned to use the inflatable bag of my father s blood pressure monitor to make a pillow. However, my parents advised me to look for an inflatable bag on the internet. When I found an inflatable bag with a pump, I covered the bag with a pillow case. The pillow system contains a flexible inflatable pillow inner and a hand inflation pump and a pillow case as shown in Fig. 14. The pressure in the inflatable pillow can be used to adjust the pillow height to slowly rebuild the cervical curvature. 12

13 (a) Inflatable pillow (b) air pump (c) pillow case (d) Inflatable pillow Fig. 14 Pillow components and pillow I made three pillows and gave these to three classmates who had the head-forward posture to check its function Rehabilitation process Training and Rehabilitation in daily life Running the training, the cervical curvature changed frequently. The initial training used low air pressure in the pillow. At that time the neck and head were relaxed. The initial state was used for some time and then the pillow was made higher to increase the cervical curvature. The weight of the head was supported by the inflatable pillow which put pressure on the cervical spine. The position does not need to be hold for a long time as it is very uncomfortable. The maximum height was set by the trainer. Figure 15 shows me using the pillow at different height. 13

14 (a) Low position Rehabilitation while sleeping: Fig. 15 Training and rehabilitation in daily life (b) High position We all spend nearly a third of our day sleeping, so this would be a good time to improve our cervical spine shape. Since cervical problems have different severities, the pillow height can be defined before handing for each person. If the pillow is too comfortable, then it is probably not helping his cervical and muscle problems. The pillow height can be chosen as follows: First put the pillow under the neck, open their valve and let out part of the air until the neck is comfortable. Then, add a little more air into the pillow to give the neck some pressure. Later, add some more air to increase the height. Three subjects used the pillows for several weeks. They told me they feel a little more relaxed. I think this will need much more time and more subjects for further research Additional Advice for Pillow Selection Some problems may arise with the pillow when it may influence the cervical curvature in inappropriate ways. (a)lying on one s back (b) Lying on the side Fig. 16 Cervical and thoracic spine shape during sleeping [6] A suitable pillow should maintain the cervical curvature while sleeping, so I put a standard spine on a pillow and drew the curve. The right pillow should have the shape shown in Fig.16 to prevent and ease cervical problems. If the cervical spine is 14

15 already distorted, the pillow can help rehabilitate the cervical spine shape. 4. Concluding Remarks First, a force analysis has shown that inappropriate posture can cause the cervical vertebra to bear greater loads which can cause cervical problems. Second, an inflatable pillow was developed to rebuild the cervical curvature. Several volunteers used the pillow for several weeks and the feedback was good. More data is needed with long term follow-up. When straightening of the cervical curvature can cause not only the muscles but also the cervical vertebra to bear larger loads. The force analysis demonstrates the differences between the loads on a natural cervical spine and a straightened one. Inappropriate posture can cause the cervical spine and the muscles to bear greater loads by generating a large moment arm. Thus, everyone should pay more attention to their posture in daily life, especially for young students who can stop cervical problems before they start. References: 1. Jia ZT, Wu QH, et al., The survey and research of the pathological change of vertebrae between teenagers, Chinese Journal of Medicine Guide, Vol. 10, No.1, 2008, P LIU HT, SHEN BZ, BU LH, et al, Analysis of the X-ray findings and etiology of adolescent cervical spondylosis and prevention cure, Progress in Modern Biomedicine, Vol. 12 No. 33 Nov., 2012, P Tan YP,Survey of research on teenagers cervical spondylosis, China Medical Hearld, 2011, Vol.8, No ISBN , THIEME Atlas of anatomy-general anatomy and musculoskeletal system 5. image